Methods are known for catalytically reducing aromatic nitroderivatives by employing, as a hydrogenation source, both molecular hydrogen and hydrogen-donor, generally carbon monoxide and water, alcohols, etc.
In particular, there have been described methods of reducing aromatic nitroderivatives, e.g. nitrobenzene to aniline by displacement of hydrogen from the carbon monoxide and water system or from synthesis gas catalyzed by cluster or carbonyl compounds of Rh, Ir, Ru and Os such as, for example, Rh.sub.6 (CO).sub.16 in the presence of various amines such as trimethylamine, N,N-dimethylbenzylamine, pyridine, N-methylpyrrolidine, N,N,N',N'-tetramethylethylene diamine, paradimethyl-aminopyridine, out of which pyridine and N,N,N',N'-tetramethyl-ethylenediamine have proved to be the most active.
Amines are generally used at a concentration remarkably higher than the concentration of the substrate (aromatic nitroderivative).
A catalyst system has been now found, which is composed by complexes of Rh, Ir, Ru and Os in the presence of or containing bidentate or tridentate nitrogen aromatic chelants never used so far, which unexpectedly provide a catalytic activity by far higher than the hydrogen displacement catalyst of the art.